The overall objectives of this research are 1) to characterize upper airway dynamics during wakefulness and sleep in patients with obstructive sleep apnea (OSA) using magnetic resonance imaging (MRI) and 2) to determine if data collected during wakefulness can predict the occurrence of OSA. OSA is characterized by recurrent partial or complete airway closure during sleep, and has important clinical implications ranging from disruption of sleep with daytime sequelae of excessive sleepiness and poor quality of life to adverse cardiovascular or metabolic outcomes. While polysomnography and studies based on measurements of airway pressures and resistance have provided a wealth of information on upper airway physiology, they are unable to assess the three-dimensional anatomy of the upper airway and its conformational changes during breathing. Knowledge of the morphology and mechanical behavior of this structure is essential for a more complete understanding of the occurrence of upper airway obstruction. Such information can be obtained with imaging technology and is the focus of this study. We propose to use state-of-the-art MRI tools to quantify upper airway dynamics in three groups of subjects: 1) OSA patients; 2) snoring volunteers; and 3) healthy age and weight-matched controls for comparison purposes. Subjects will undergo MR imaging to assess upper airway morphometry and changes in airway size during tidal breathing both during wakefulness and natural sleep with simultaneous measurement of nasal-oral flow partition and sleep state and stages. Dynamic patient-specific models of upper airway morphometry will be reconstructed from the MR images from which various anatomical markers will be calculated. Differences in these markers between groups and between stages (awake vs. asleep) will be evaluated. The proposed studies of characterizing the conformational change of the upper airway during tidal breathing will provide a new means of identifying geometrical abnormalities that lead to airflow obstruction. This proposal is a first step in addressing a currently unmet clinical need for treatment guidelines tha take into account the dynamic nature of the upper airway. Completion of these studies will also lay the groundwork for future modeling studies that will combine patient-specific upper airway dynamics with detailed flow simulations to provide better insight in biomechanical properties of the upper airway and flow-driven mechanisms on which to optimize therapeutic treatment. The methods developed in this research will be directly applicable to all patient populations with upper airway dysfunction.